Alkaline primary battery and electrolyte therefor



June 1954 A. DENISON ET AL ALKALINE PRIMARY BATTERY AND ELECTROLYTE THEREFOR Original Filed Oct. 17, 1945 I2 INSULATION) 22 (ELECTROLYTE) l0 ZINC) l6 (CONDUCTOR) FIG.

l2 (INSULATION) 24 (FILLER MATERIAL) 20 I (SILVER FEROXIDEJW2 02) IO( ZING) l6 (CONDUCTOR) E w m c E L E E w n s O P N w M M m F FIG.3.

INVENTORS IRVING A.DENI$ON PAUL L. HOWARD a 7 ATTORNEY-S AMPERE HOUR Patented June 15, 1954 ALKALINE PRIMARY BATTERY AND ELECTROLYTE THEREFOR Irving A. Denisom, Silver Spring, Md., and Paul L. Howard, Arlingtomva.

Original application October 1'7, 1945, Serial No.

622,920, now Patent No.

2,513,292, dated July 4, 1 9,50. Divided and this application May 5, 19.50, Seria1N0. 160,204

(Granted under Title 35, U. S. Code (1952),

see. 266.)

10 Claims.

This application is a division of application Serial No. 622,920, filedi October 1?, 1945, for Alkaline Primary Battery and Electrolyte There.- for, which has matured into Patent No. 2,513,292, granted July 4, 1950.

The inventiondescribed herein may be made and used by or for the Government of the United States for governmental purposes without the payment to us of any royalties thereon or therefor.

Our invention, relates to an improved alkaline primary battery. More specifically we disclose a primary battery using a high normality alkaline electrolyte with an agent to counteract the effect of soluble ionic and colloidal positive electrode particles from either dispersing into the electrolyte or depositing on the negative electrode.

Batteries are known in the prior art, using a consumable zinc electrode together with an alkaline electrolyte. However, such cells have suffered from the, disadvantage that increased normality of alkaline electrolytes results in increased corrosion of the zinc. This results from the transferring of positive particles to the zinc causing a further reduction of wet shelf life particularly where readily reducible positive electrodes are used to reduce polarization. Prior art batteries have also suffered from the disadvantages of being able to produce only a portion of' the theoretically available energy and to operate at reducedefliciency at both low and elevated tem- 'peratures.

In accordance with our invention an alkaline electrolyte with an added agent is disclosed which effectively increases the wet shelf lifeof an alkaline primary battery;

Also in accordance, with; our invention a battery is produced having the ability to withstand a high continuous rate of discharge without appreciable decrease in voltage.

Further, in accordance with our invention, provision is made for restricting the circulation of electrolyte about the electrodes.

Our invention is further characterized by the provision of means to prevent the dissolving of anode and cathode material by the electrolyte.

Another feature of our inventionresides in the fact that an extremely large share of the theoretical capacity of the battery may be utilized.

Still another characteristic of the battery structure which we disclose is the light weight per. ampere hourxof capacity. 1 A still further characteristic of our invention resides in the fact that the desirable, discharge characteristics; are maintained. in. spite of operation at the. extremes of temperature likely to, be encountered in use.

Our invention also resides, in features of construction, combination and arrangement herein described or disclosed.

In the drawings;

Figure 1 is a section view of one embodiment of a battery constructed in accordance with our teachings;

Figure 2 is a sectional view of a preferred embodiment using a filler material in the electrolyte. chamber and an electrolytic silver peroxide anode.

Figure 3 is a characteristic plot showing the discharge curve of a battery of the, type shown in Figure 2.

In Figure 1 the battery case I a consists of a zinc can which servesas the outer negative electrode. Suspended within the can, for exam le, by means of insulation I2, is the electro-positive electrode M which, in our preferred embodiment, may have a metallic core l-S, brought out to a terminal IS. The space 22 between the electrodes is occupied by the electrolyte which preferably consists of sodium hydroxide together with certain buffering compounds which will be described in detail below.

Figure 2 shows structure similar to that in Figure 1 except for the addition of filler material 24 which preferably consists ofnylon, polystyrene, chopped asbestos or similar inert material. In this embodiment the active positive electrode consists of an electrolytic silver peroxide body 20 of the formula Ag202.

Many primary battery applications require a high discharge rate at asubstantially constant voltage and a slow rate of deterioration upon standing in the wet condition during a period of storage or dormancy. Such applications are particularly numerous in military and naval equipment where light weight and dependability after a period of storage are of paramount importance.

In. order to prevent corrosion during storage, various, means have been devised for releasing the electrolyte immediately prior to use. This has been accomplished, for example, by the breakage of a breakable glass container or diaphragm. The use of such batteries, however, is accomplished by the, disadvantage that a mechanical force is required to accomplish the re lease of the electrolyte and further that corrosion takes place at, a highrate during the dormancy period between periods of intermittent heavy discharge. Further, such batteries cannot be. made of optimum size. since separate proaccompanied by certain novel used as the positive electrode. the reaction taking place at the electrolytically the zinc electrode.

solved by the solution, entering the solution as ion concentration plus an a salting ou effect.

: terials act as buffers in maintaining the hydroxyl ion concentration substantially constant.

' amounts.

visions must be made for the storage of the electrolyte out of contact with the electrode.

An inherent requirement of a battery having 'a high discharge rate is an active negative elec trode and a plentiful supply of ions in the electrolyte. The use of zinc, zinc alloy or zinc containing material as the consumable negative electrode is desirable since zinc is a fairly active metal and is both inexpensive and widely used in battery manufacture. Because of the high ionic dissociation of sodium hydroxide, potassium hydroxide and similar alkali metal hydroxides, water solutions of these compounds are normally considered satisfactory electrolytes. To produce a workable battery the zinc and alkaline hydroxide require in addition an electrode electropositive to zinc and a supply of oxygen to prevent polarization of the cell. For example, we have found that electrolytic silver peroxide is advantages when The equations of formed silver peroxide electrode are as follows: (1) Ag2O2+Ag2O+O=+le AgzO- 2Ag+0=+1e Thus for total reaction, Equations 1 and 2 give 3 below:

Ag2Oz+2Ag+2O=+2e As stated above the use of a concentration of the hydroxide electrolyte sufliciently great to enable a high discharge rate seriously corrodes In this case the zinc is diszinc hydroxide. The corrosion of the zinc electrode is aggravated by any impurity in or on the zinc tending to set up electric couples thereby producing local action. In the case of the positive electrode, it has been found that, for example, where a silver peroxide electrode is used both silver peroxide and silver oxide enter the solution in the ionic and colloidal state; however,

this solubility is small.

- p The zinc electrode cannot be protected from these silver lonic and colloidal particles in the ,electrolyte by conventional separators or special semipermeable films because of the minute par- .ticle size.

As previously stated it is necessary to prevent the transference of such particles in order to maintain the zinc electrode free from undue corrosion. Thus it is necessary to have an electrolyte compound of the proper hydroxyl additional ingredient which has the property of collecting the colloidal and ionic silver into conglomerates of such a stated above on the Such an' ingredient is herein termed a "salting out medium and the action In addition, these ma We have found that the salting out effect may be accomplished with a number of materials to be described. In a typical application satisfactory results have been attained with an electrolytic silver peroxide positive electrode and zinc negative electrode in an alkaline medium to which these materials are added in varying In addition to conventional alkaline hydroxides, water solutions of alkali metal ethylates with or without additional ingredients disclosed below are effective. The materials found preparation without appreciably affecting the I salting out and buffering action.

Example 1.-Potassium ethylate Potassium ethylate was prepared from potassium hydroxide and ethyl alcohol combined in molecular proportions with the addition of a small amount of water to facilitate solution of the hydroxide. The reaction proceeds according to the equation The solution was refluxed for several hours and evaporated to a pasty condition to form the potassium ethylate used in making up the electrolyte. Sodium hydroxide may be substituted for potassium hydroxide if desired. A satisfactory electrolyte was formed using 30% to 60% of the alkali ethylate in water solution alone. It was found that the addition of from 3% to 35% zinc oxide or from 7% to 35% boric acid increased the salting out effect.

Example 2.Sodium hydroxide-sodium zincate solution A solution of sodium zincate in sodium hydroxide was prepared in the following manner: Zinc hydroxide prepared by precipitation from zinc chloride by ammonium hydroxide was shaken for 12 hours with a solution containing an equivalent amount of sodium hydroxide to react according to the equation After warming on the water bath for two hours, the solution was filtered. Equal parts of the filtrate and water by volume were added to a 14 normal sodium hydroxide solution in such proportions to produce a solution with a pH value Satisfactory sodium zincate solutions were formed in accordance with the above reaction using from 10 to 50% of sodium hydroxide with 3% to 35% zinc hydroxide. If potassium hydroxide (10% to 50%) is used in place of the sodium hydroxide, the range for zinc hydroxide is 1% to 5%.

Example 3.Sodium hydroxide-Doric acid solution With the object of preparing a buffer solution of sodium hydroxide having relatively low pH value, various amounts of boric acid were dissolved in 25 milliliter portions of 14 normal sodium hydroxide. The reaction is believed to proceed as follows:

HaBO3+3NaOH Na3BO3+3H2O .or HsBO3+NaOH+NaBO2+2H2O v A solution consisting of 1.87 grams of boric acid in 25 milliliters of 14 normal sodium hydroxide solution resulted in a pH value of 9.25.

It was found that an electrolyte may be formed in accordance with the above reaction using from -10% to 50% alkali metal hydroxide with 7% to 35% boric acid.

The use of a buffer is known in the art in conassua e nectlon with 'other chemical "reactions, -*especially those encountered in qualitative and quantita- "tive analysis; Upon depletion of the -hydroxyl ions'during the use of the battery, additional hydroxyl ions are supplied by'the hydrolysis of the "While the-use of a salting "outsolutionresults "in -a marked decrease of electrode deterioration, a further improvement canbe obtained by the "use of a filler-material ito prevent freecircula- {tionvo'f-the electrolyte. In-the case of the negative-zinc electrode, reduction of "circulationsresults the holding of zinc ions near the electrode--thereby causing an increase of zinc hydroxide :in "solution to the extent that formation of further zinc ionsis inhibited. This enables relatively high hydroxyl ion concentration to be used without excessive corrosion of'the zinc. We have found that asbestos in the chopped or fibrous form, nylon fiber; polystyrene fiber, or. similar inert materials allowing thepassage of ionic current 'but inhibiting-circulation and migration of the coagulated colloidal particles are satisfactory filler materials. 'Thematerial should pref- --.er-ably have nacheniical reducing efiect'on the positive electrode.

-As previously stated in the above example we have "found that electrolytic silver peroxide is extremelysuitable asapositive electrode mate- =rial, particularly because of its readily reducible nature. The chemical reactiontaking place in the cell using electrolytic silver peroxide and zinc electrodes .is probably expressed by .the following reactions:

The suitability of silver peroxide as avpositive electrode material has been found to "be somewhat :dependent on the method of formation. 3

:It:-has been found that desirable characteristics are obtained when the silver peroxide is formed electrolytically from *a'pure silver "electrode. The process of formation (using the silveraelectrode :as the positive pole .is 'believedto take .place in two steps: first, the production of silver oxide. secondly, the production of the peroxide from the oxide. This is indicated by the formation curve shown in Figure 3. It is believed that the rises in voltage during formation are respectively due to the complete formation of silver oxide from silver, and the complete conversion of the lower oxide to the peroxide form.

Satisfactory positive electrodes have also been produced by applying silver oxide in paste form on a metallic screen or other backing, reducing to silver either electrolytically or by means of a flame, and oxidizing electrolytically to the silver peroxide as discussed above. Electrolytic formation is believed advantageous because of the spongy texture of the peroxide formed. Other means of forming the silver peroxide positive electrodes will appear to those skilled in the art. For example, silver peroxynitrate of the formula Ag7NO11 may be used as a starting material and reduced by some means, for example the application of hot water, to form silver peroxide. However, such chemical methods do not produce a, low resistance electrode comparable to that produced electrolytically.

The desirability of using a filler material to inhibit the corrosion-of-the:negativeelectrodeihas been discussed; however, we have found that filler material utilized in accordance without teachings can also beused to greatly-reducecorrosion of the positive electrode. The high-concentration-of sodium hydroxide tends "to-sattack the silver peroxide :positive- :electrode for itwo reasons: first, because of the-solubility oflbo'th silver oxide and :silver peroxide in strong :con-

centrations of sodium hydroxide; secondly, be-

cause high .hydroxyl ion concentration encourages the dispersion of silver oxide and silver peroxide from the parent masssin colloidalxform.

Such-colloidal material unless impeded gradually driftstosthe zinc electrode where it.combines wlth the zinc zto aggravate the corrosion at theanega- .tive electrode. Various .typesrof 'cellulosic1.materials :were investigated in :order ,tO-zDIOdUQfi-fl :barriernpervious to ions but WhiGh:W01l1d impede nolloidalparticles. .;It was :found however athat .lthenuse .ofrcellulosic :materials was not desirable since the barrier :material acted :as a reducing agent, reducing the silver oxides to metallic-silver and :thus adversely affecting :the positive elecilllOdB.

Ilhus it is seen v,that theme ;of .a ,salting out material aids in reducing the colloidal drift: since as indicated byoursstudies, the acid ion causes the a gregation of the colloidal particles :to par- .ticlesof such a size that the migration is more easily inhibited by the filler material.

.Both sodium hydroxide andpotassium hydroxide have been mentioned above .as a plentiful source of .hydroxylions, However, in ourpreferred emb-odiment wehave usedsodium hydroxide since the zincate formedat the timerofdischarge is morelsoluble insodium hydroxide :than potassium hydroxide. Stated another way suf ficient zincate can beadded to the battery ini- .tially toserve as an effective buffer without ap proaching the saturation point. Thus :as .the zincate .is ,formed during the discharge it will be soluble and not 'causea lowering --of .battery capacity. If potassium hydroxide is used with p a zincate bufferit is necessary to use aupracti- .cally 'saturated solution of zincate .to obtainsufficientcbuifering action. Thus zincate entering the solution as a result of discharge willreach saturation :and start to precipitaterearly in the discharge. Such precipitation. reduces the effective plate area available for discharge.

In Figure 3 two typical discharge characteristic curves are given. It will be seen that either a silver oxide or an electrolytic silver peroxide positive electrode results in a practically constant voltage discharge curve. The advisability of using an electrolytic silver peroxide is indicated graphically by the fact that the area under the silver peroxide curve is more than 50% greater than that under the silver oxide curve, indicating a greatly increased energy output where an electrolytic silver peroxide is used. No break in the discharge curve occurs as the peroxide changes to the simple oxide form. We have found that a slow electrolytic formation of the silver peroxide anode causes increased available energy for a given weight of battery material.

It will be seen from the above that we have produced a battery having distinct advantages over batteries used in the prior art, particularly with regard to shelf life, sustained voltage during high rates of discharge, and available energy per unit weight. We have shown a specific mechanical construction in Figures 1 and 2; however',.it will be obvious to one skilled in the art follow in the true spirit and scope of our invention.

What we claim is: 1. An electric battery comprising a negative electrode of zinc containing material, a positive electrode of an electrolytically formed silver peroxide, an electrolyte of a Water solution of an alkali metal hydroxide, and a salting out compound consisting of a weak acid formed from a non-metallic oxide of the type producing hydroxyl ions upon hydrolysis, whereby the hydroxyl ion concentration may be maintained at a substantially constant value.

2.An electric battery comprising a first electrode of zinc-containing material, a second electrode of electrolytically formed silver peroxide,

an electrolyte including an alkali metal hydroxide with a salting'out medium and a porous barrier in said electrolyte between said electrodes whereby the migration of colloidal electrode material from one electrode to the other is inhibited.

3. An electric battery comprising a zinc-comtaining negative electrode, a positive electrode including electrolytic silver peroxide, a solution of alkali metal hydroxide, a porous inert barrier in said solution between said electrodes and a weak acid formed from a non-metallic oxide dissolved in said solution whereby the conglomeration of colloidal particles in said solution caused by the acid radical of said weak acid enables said porous barrier to more efiectively prevent migration of colloidal particles between said electrodes.

4. An electric battery comprising a zinc negative electrode, an electrolytic silver peroxide positive electrode, an electrolyte comprising sodium hydroxide, boric acid, and a porous barrier between said electrodes in contact with said electrolyte.

5. The subject matter as claimed in claim 4, said barrier comprising asbestos.

6. An electric battery comprising azinc negative electrode, an electrolytic silver peroxide electrode and an electrolyte including 10 to 50% alkali metal hydroxide, 7 to 35% boric acid, and the remainder water. 7 I

7. An electric battery comprising a. negative electrode of zinc containing material, a positive said solution whereby the conglomeration of colloidal particles in said solution caused by the acid radical of said weak acid enables said porous barrier to more eiiectively prevent migration of colloidal particles between said electrodes.

9. An electric battery comprising a zinc negative electrode, a positive electrode containing an oxide of silver, an electrolyte comprising an alkali metal hydroxide, boric acid, and a porous barrier between said electrodes in contact with said electrolyte.

10. An electric battery comprising a zinc negative electrode, a positive electrode containing an, oxide of silver and an electrolyte including 10% to 50% alkali metal hydroxide, 7 to 35% boric acid, and water.

References Cited in the file of thi patent UNITED STATES PATENTS Number Name Date 692,298 Waldemar Feb. 4, 1902 793,078 Hubbell June 27, 1905.

1,675,828 Siegmund July 3, 1928 2,422,045 Ruben June 10, 194'! 2,561,943 Moulton July 24, 1951 V FOREIGN PATENTS Number Country Date 95,423 Switzerland May 30, 1921 

1. AN ELECTRIC BATTERY COMPRISING A NEGATIVE ELECTRODE OF ZINC CONTAINING MATERIAL, A POSITIVE ELECTRODE OF AN ELECTROLYTICALLY FORMED SILVER PEROXIDE, AN ELECTROLYTE, OF A WATER SOLUTION OF AN ALKALI METAL HYDROXIDE, AND A SALTING OUT COMPOUND CONSISTING OF A WEAK ACID FORMED FROM A NON-METALLIC OXIDE OF THE TYPE PRODUCING HYDROXYL IONS UPON HYDROLYSIS, WHEREBY THE HYDROXYL ION 